A conventional angular ball bearing is equipped with an outer ring, on the inner circumferential surface of which a raceway surface is provided; an inner ring, on the outer circumferential surface of which a raceway surface is provided; and a plurality of balls provided between the raceway surfaces so as to be rotatable at a contact angle. This kind of bearing is built in various heavy mechanical apparatuses, such as speed reducers for industrial robots and construction machines.
In recent years, as these heavy mechanical apparatuses have been made smaller in size and lighter in weight, this kind of bearing has also been required not only to be made lower in cost but also to be made lighter in weight. For the purpose of cost reduction and weight reduction, as in the case of an angular ball bearing 30 shown in FIG. 5, the axial dimensions of the outer ring 31 and the inner ring 32 thereof have been made smaller.
In this angular ball bearing 30, the axial dimensions of the outer ring 31 and the inner ring 32 are made smaller, a counter bore 31b is formed on one side of the raceway surface 31a of the outer ring 31, and a counter bore 32b is formed on the other side of the raceway surface 32a of the inner ring 32; furthermore, since the axial dimensions of the outer ring 31 and the inner ring 32 are made small, a portion of each ball 33 protrudes from the axial end face of the outer ring 31 or the inner ring 32.
When this kind of bearing is produced, in particular, in an assembly process or a conveying process, the plurality of angular ball bearings 30 having been assembled are stacked in the axial direction, whereby, as shown in FIG. 6, the above-mentioned protruding portion of the ball 33 of one bearing makes contact with the outer ring 31 or the inner ring 32 of the bearing that is stacked thereon, and the surface of the ball 33 is likely to be damaged.
Hence, for the purpose of preventing the ball 33 from being damaged, as a conventional angular ball bearing, an angular ball bearing is known (for example, refer to Patent Document 1) that is characterized in that the bearings are stacked by using the retainers thereof for support purposes during storage and conveying.